The protection switching is essentially a survivability technology. The survivability technology is a technology for improving the reliability of a network by providing an ability of service restoration from service interruption. This technology is supposed to be applied to all ring communication networks, to which protection switching is necessarily required.
The protection switching is widely applied in the communication networks. For example, SDH/SONET(Synchronous Digital Hierarchy/Synchronous Optical Network) provides the protections of 1+1, 1:N(one to many), two-fiber ring/four-fiber ring multiplex section protection, SNCP(Sub-network Connection Protection) and DNI(Dual-Node Interconnection) protection. OTN(Optical Transport Network) also have all types of above protection.
However, the protection switching in each of the above mentioned communication networks does not relate to the M:N protection mode which denotes a mechanism where M protection channels serve to protect N working channels. In a communication network, the anti-failure ability of a protection channel is typically same as that of a working channel, so their failure probabilities should also be the same. Thus, in the case that the 1:N protection is adopted and N is large, the probability of several working channels contesting for one protection channel may be high. In this case, the network can not provide protection for some of the working channels. Accordingly, it is necessary to promote the M:N protection, in which the relation between M and N is: 1<=M<=N, in communication networks.
For this reason, the US patent application US 2004/0022279 A1 presents a corresponding implementation method for M:N path protection, and the EP patent application EP1014613 A2 proposed a structure and function of network nodes for performing M:N protection switching. However, neither of the two patent applications provides a complete solution for M:N protection switching.
Wherein, US 2004/0022279 A1 describes an M:N path protection method. In the M:N path protection method provided by this patent application, use is made of the tandem connection monitoring function, the tandem connection reverse defect indication and the tandem connection trail trace identifier. Particularly, upon detection of a failure on the working channel segment, the occurrence of this failure is communicated to the far end node by inserting forced RDI (Remote Defect Indication) into the tandem connection as long as the failure persists. In the case of more than one protected paths, the failed path is identified by means of the unique trail trace identifier received on the protection channel. In the case of several protection channels, one network node is defined as slave node which has to follow the switch-over initiated by the master node and choose the same protection channel as the master node. A combination of two timers is used to enable return from failure condition to normal operation.
Furthermore, the patent application EP1014613 A2 describes a structure and function of network nodes for performing M:N protection switching. A node of M:N ring network includes an optical switch array for the bridging(Dual-fed) and switching(selective-receipt) of optical signal. The optical switch array includes a number of separate optical switching networks, each of which corresponds to a protection channel and is connected to a protection optical port through an optical transceiver. Within the node, the protection channels can be changed respectively by changing the respective optical switch networks. A multiplexer and a de-multiplexer are also included, for the switching between the signals received from the optical ports and the signals processed by the optical switch array. A fault detector is used to detect the fault of signals after the signals are de-multiplexed. There are at least two nodes in a network. The two nodes are connected through two optical fibers for transmitting working traffic and protection traffic respectively. This patent application provides a method for routing protection traffic which is to enable at least two protection channels to provide protection for a number of working wavelength.
In consideration of this, an M:N protection switching technology of ring network is presented, wherein, the signaling interaction is performed by the transferring of switch protocol signaling on a protection channel or a private control channel through overhead bytes or special messages, thereby the protection switching of ring network is implemented. This technology provides support for external switching commands such as FS, MS, LP, etc., provides support for the configuration of the priority of a protection channel, and provides support for protection when the protection channel has a different bandwidth from that of the working channel. The protection channel has the functions of transmitting extra traffics and the like, can provide protection in the event of failure of several working channel, can optimize the long and short path protection channels to be used for protection of a working channel at the same time, thus providing a perfect protection switching. This technology provides a powerful method for realizing the M:N protection switching of ring network. However, this technology doesn't provide a specific definition of signaling and the transmission method thereof during the protection switching of ring network.